2.1.  Requirements classes defining resources

Requirements Class “Core” (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/core)

The Core specifies requirements that all Web APIs have to implement if they are claiming to support tiles from a geospatial resource following this OGC API — Tiles Part 1: Core standard. It defines how to retrieve individual tiles by building a URI from three variables corresponding to the tile matrix, tile row and tile column for that tile.

Table 1 — Overview of resource and common direct link that corresponds to tiles defined in core conformance class

Requirements Class “TileSet” (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/tileset)

The tileset conformance class defines a mechanism to describe a tileset using a specific tile matrix set and obtain a templated link to individual tiles.

Table 2 — Overview of resources and common direct links that correspond to the tileset

Requirements Class “TileSets List” (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/tilesets-list)

The tilesets list conformance class defines a generic operation to retrieve a list of tilesets, without association to any particular type of resources.

Table 3 — Overview of resource and common direct link that corresponds to the tileset list

2.2.  Requirements classes defining data origins

Requirements Class “Dataset TileSets” (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/dataset-tilesets)

The dataset tilesets conformance class allows retrieving tiles for a whole dataset potentially made up of multiple geospatial data resources. All Web APIs have to implement this conformance class if they are claiming to support dataset tiles following this OGC API — Tiles Part 1: Core standard. Dataset tiles may combine content from multiple geospatial resources, regardless of whether those are available separately (as tiles or otherwise).

Table 4 — Overview of resource and common direct links that corresponds to the dataset tileset

Requirements Class “GeoData TileSets” (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/geodata-tilesets)

The geodata tilesets conformance class allows retrieving tiles from a specific geospatial data resource.

Table 5 — Overview of resource and common direct links that corresponds to the geospatial data resources tilesets

2.3.  Requirements classes defining query parameters

Requirements Class “Collections Selection” (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/collections-selection)

The tiles geodata selection conformance class allows to list specific geospatial data resources from which to retrieve tiles, e.g. for use with data set tiles.

Table 6 — Overview of resource and common direct links that corresponds to the geodata selection

Requirements Class “DateTime” (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/datetime)

The datetime conformance class specifies how to provide tiles in a domain that has a generic time dimension.

2.4.  Requirements classes for specific resource representations

Requirements Class “OpenAPI Specification 3.0 API definition” (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/oas30)

The OpenAPI Specification 3.0 conformance class specifies requirements for an OpenAPI 3.0 definition in addition to those defined in OGC API — Common — Part 1: Core.

Requirements Class “XML TileSet Metadata” (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/xml)

The XML conformance class specifies how to use XML as an alternative encoding for describing tilesets.

Requirements Classes for tile encodings

This standard does not mandate a specific encoding or format for representing tiles and remains flexible and extensible to other formats that users and providers might need. However, requirements classes are provided for the following common tile formats:

• PNG (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/png)

• JPEG (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/jpeg)

• TIFF (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/tiff)

• NetCDF (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/netcdf)

• GeoJSON (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/geojson)

• Mapbox Vector Tiles (http://www.opengis.net/spec/ogcapi-tiles-1/1.0/req/mvt)

All these conformance classes act as building blocks that should be implemented in combination with other more fundamental conformance classes that provide support for Web API discovery, conformity and Web API formal definition (e.g., OpenAPI). Possible alternatives for these fundamental conformance classes are OGC API — Common Part 1: Core, OGC API — Features Part 1: Core or any other non-OGC classes that provide this functionality.

All requirements-classes and conformance-classes described in this document are owned by the standard(s) identified.

2.5.  Declaration of conformance

Conformance with this standard shall be checked using all the relevant tests specified in Annex A (normative) of this document if the respective conformance URLs listed in Table 7 is present in the conformance response. The framework, concepts, and methodology for testing, and the criteria to be achieved to claim conformance are specified in the OGC Compliance Testing Policies and Procedures and the OGC Compliance Testing web site.

Table 7 — Conformance class URIs

4.1.  Terms and definitions

This document uses the terms defined in Sub-clause 5.3 of OGC Web Services Common (OGC 06-121r9), which is based on the ISO/IEC Directives, Part 2, Rules for the structure and drafting of International Standards. In particular, the word “shall” (not “must”) is the verb form used to indicate a requirement to be strictly followed to conform to this standard.

This document also uses terms defined in Sub-clause “Terms and Definitions” of OGC API — Common, Part 1: Core.

For the purposes of this document, the following additional terms and definitions apply.

4.1.1. coverage tile

tile that contains information, often in a gridded form, where the values represent observations or measurements as a count, or quantity using some unit of measure

4.1.2. dataset

a set of data, published or curated by a single agent, and available for access or download in one or more representations (modified from DCAT: https://www.w3.org/TR/vocab-dcat-2/#dcat-scope).

4.1.3. geospatial data resource

web resource that consists in a set of geospatial data

4.1.4. geospatial aspect

web resource that represents a component of geospatial information (metadata, schemas…​) or geospatial data accessed using a particular mechanism and data model (e.g., feature items, tiles, maps, coverages,…​) of a more generic geospatial data resource (e.g., a collection)

4.1.5. map tile

tile that contains information in a gridded form where the values of cells are colors which can be readily displayed on rendering devices

4.1.6. tile

geometric shape with known properties that may or may not be the result of a tiling (tessellation) process. A tile consists of a single connected “piece” without “holes” or “lines” (topological disc).

In the context of a 2D tile matrix, a tile is one of the rectangular regions of space, which can be uniquely identified by a row and a column integer indices, making up the tile matrix.

In the context of a geospatial data tile set, a tile contains data for such a partition of space as part of an overall set of tiles for that tiled geospatial data.

4.1.7. tile matrix

tiling grid in a given 2D coordinate reference system, associated to a specific scale and partitioning space into regular conterminous tiles, each of which being assigned a unique identifier

4.1.8. tile matrix set

tiling scheme consisting of a set of tile matrices defined at different scales covering approximately the same area and having a common coordinate reference system.

4.1.9. tile indexing scheme

scheme allowing to uniquely reference a tile in a tiling scheme by the use of a unique identifier (or set of identifiers), and reversely, which unique identifier (or unique set of identifiers) corresponds to a space satisfying the geometric properties of a specific tile

4.1.10. tile set

a set of tiles resulting from tiling data according to a particular tiling scheme

4.1.11. tiling scheme

scheme that defines how space is partitioned into individual tiles, potentially featuring multiple levels of detail (each tiling at a different granularity to reflect a different resolution or scale)

A tiling scheme defines the spatial reference system and the geometric properties of each tile defined by the scheme. Those properties include which space each tile occupies, i.e. its extent, as well as a tile coordinate origin if a particular corner of origin convention is established.

4.1.12. tile set metadata

additional metadata beyond the common properties defining the tile set. Such metadata could be an abstract, the owner, the author, or other common metadata. [OGC 19-014r3]

metadata describing common properties defining a tile set, layers and styles used to produce the tile set, the limits of the tile matrix with actual data and common metadata such as abstract, owner, author, etc.

4.1.13. vector tile

tile that contains vector information that has been generalized (simplified) at the tile scale resolution and clipped by the tile boundaries.

4.1.14. Web API

API using an architectural style that is founded on the technologies of the Web [source: OGC API — Features — Part 1: Core]

5.1.  Identifiers

The normative provisions in this standard are denoted by the URI http://www.opengis.net/spec/ogcapi-tiles-1/1.0 .

All requirements and conformance tests that appear in this document are denoted by partial URIs which are relative to this base.

5.2.  Link relations

To express relationships between resources, RFC 8288 (Web Linking) is used.

The following IANA link relation types are used in this document:

• alternate: Refers to a substitute for this context.

• self: Conveys an identifier for the link’s context.

• item: The target IRI points to a resource that is a member of the collection represented by the context IRI.

• service-desc: Identifies service description for the context that is primarily intended for consumption by machines. (Web API definitions are considered service descriptions)

• service-doc: Identifies service documentation for the context that is primarily intended for human consumption.

The following link relation types specified in the Two Dimensional Tile Matrix Set and Tileset Metadata standard are used:

• http://www.opengis.net/def/rel/ogc/1.0/tiling-scheme: The target IRI points to a resource that describes the TileMatrixSet according to the 2D-TMS standard.

• http://www.opengis.net/def/rel/ogc/1.0/dataset: The target IRI points to a resource representing the dataset (e.g., the root of an OGC Web API).

• http://www.opengis.net/def/rel/ogc/1.0/geodata: The target IRI points to a resource representing a collection of geospatial data.

In addition, the following link relation types are used for which no applicable registered link relation type could be identified:

• http://www.opengis.net/def/rel/ogc/1.0/tilesets-vector: The target IRI points to a resource that describes how to provide tile sets of the context resource in vector format.

• http://www.opengis.net/def/rel/ogc/1.0/tilesets-map: The target IRI points to a resource that describes how to provide tile sets of the context resource in map format.

• http://www.opengis.net/def/rel/ogc/1.0/tilesets-coverage: The target IRI points to a resource that describes how to provide tile sets of the context resource in coverage format.

• http://www.opengis.net/def/rel/ogc/1.0/tiling-schemes: The target IRI points to a resource that lists one or more TileMatrixSets according to the 2D-TMS standard.

Used in combination with OGC API — Features — Part 1: Core or OGC API — Common - Part 1: Core, other link relation types will be used, including:

• http://www.opengis.net/def/rel/ogc/1.0/conformance: Refers to a resource that identifies the specifications that the link’s context conforms to.

Used in combination with OGC API — Features Part 1: Core or OGC API — Common Part 2: Geospatial data, other link relation types will be used, including:

• http://www.opengis.net/def/rel/ogc/1.0/data: Refers to the list of collections available for a dataset.

Each resource representation includes an array of links. Implementations are free to add additional links for all resources provided by the Web API.

5.3.  Use of HTTPS

For simplicity, this document in general only refers to the HTTP protocol. This is not meant to exclude the use of HTTPS and simply is a shorthand notation for “HTTP or HTTPS.” In fact, most servers are expected to use HTTPS, not HTTP.

6.1.  Introduction

The OGC API — Tiles standard defines building blocks which can be used in a Web API to retrieve geospatial data as tiles that follow the structure defined in OGC 17-083r4 2D Tile Matrix Set and Tileset Metadata standard (see Clause 7). The text in this document assumes that the reader is familiar with the concepts in the OGC 17-083r4, such as tile, tile set, tile set metadata, tile matrix and tile matrix set. If that is not the case, reading the overview subsection in the OGC 17-083r4 first is recommended.

Services and clients are encouraged to support as many of the TileMatrixSets defined in the OGC 17-083r4 Annex D and E, as well as others in the OGC TileMatrixSet registry as possible for all geospatial data resources to maximize interoperability. However support for any specific tile matrix set is not required. Tiles that share the same tile matrix set can be easily presented together in a data integration client.

The OGC API — Tiles standard is a successor to the OGC’s previous Web Map Tile Service (WMTS) standard [10]. The essence of the tile matrix set has not changed from the original one used in WMTS, so tiles generated by a WMTS and the ones generated by an implementation of this OGC API that are based on the same tile matrix set can also be easily represented together. If the selected tile matrix set is the one called WebMercatorQuad (see OGC 17-083r4 Annex D.1), tiles are also compatible with the ones made available by some popular mass market approaches (despite concerns repeatedly raised on the accuracy of the CRS used in WebMercatorQuad).

Figure 1 — Contiguous tiles from different services and APIs sharing same WebMercatorQuad tile matrix set and the tile matrix identified as 15 (sometimes called "zoom")

This document does not specify any requirement for the type of geospatial data resource that could be delivered as tiles. Provided that the geospatial data resources can be organized into tiles, they can be supported regardless of whether they are maps, features data, coverages, a resource that does not represent data per se (e.g., an annotation) and so forth.

These geospatial data resources can advertise one or more lists of available tilesets (see Clause 8 and Clause 9). This standard also defines how to link to tilesets originating from two specific data resources: OGC API datasets (see Clause 10) and collections (see Clause 11), but other OGC APIs can provide other possibilities. Accessing the geospatial data resource content (other than as tiles) or its descriptions is possible but out of the scope of this standard. If a description of the geospatial data resource is specified by another standard, and this description has a mechanism to add links to other resources, this standard indicates the need to add a link to the list of available tilesets.

The OGC API Tiles API standard does not specify how to get a Web API definition, the conformance class list or the collections lists. However, the standard assumes that the first two are defined by an OGC API standard (e.g., OGC API — Common — Part 1: Core) and the latter by an OGC API for collections (e.g., OGC API — Common — Part 2: Geospatial data). A similar definition is provided directly by OGC API — Features — Part 1: Core.

6.2.  Evolution from OGC Web Services

OGC Web Service (OWS) standards have historically implemented a Remote-Procedure-Call-over-HTTP architectural style using Extensible Markup Language (XML) for payloads. This was the state-of-the-art when some of the initial versions of OGC Web Services were originally designed in the late 1990s and early 2000s. This architectural style has now a competing RESTful Web API style that is proposed as an alternative to RPC pattern. A RESTful Web API style is resource-oriented instead of service-oriented. The Web Map Tile Service 1.0 already defines a resource oriented architectural style but it lacks a Web API definition. This OGC API — Tiles standard specifies a Web API that follows the Web architecture and in particular the W3C/OGC Best Practices for sharing Spatial Data on the Web [8] as well as the W3C Best Practices for sharing Data on the Web [9]. The bibliography lists several engineering reports from initiatives that led to the development of OGC API — Tiles. Some of the engineering reports are from OGC Testbed initiatives [1] [16] , whereas others are from the OGC Vector Tiles Pilot [3] [4] [5] [6] [7].

This document provides the necessary elements to incorporate tile support to a Web API implementation. These elements can be incorporated in an API based on the OGC API — Features — Part 1: Core or can be incorporated in a Web API implementation based on the OGC API — Common — Part 1: Core. Both specify a kernel of a Web API approach to services that follows current resource-oriented architecture practices in the OGC. The OGC API — Common standard provides the foundation upon which implementations of the OGC APIs can be built. OGC API — Common can be combined with this standard and other resource-specific OGC API standards to build an OGC API implementation. However, this standard is done in a way that can extend OGC API — Common, but does not make OGC API — Common mandatory. This way, this standard can be reused as a building block in other APIs that does not follow the OGC API pattern.

Beside the general alignment with the architecture of the Web (e.g., consistency with HTTP/HTTPS, hypermedia controls), another goal for OGC API standards is modularization. This goal has several facets:

• Clear separation between core requirements and more advanced capabilities. This OGC API — Tiles — Core standard presents the requirements that are relevant for almost everyone who wants to share or use Tiled Data on a fine-grained level. Additional capabilities that several communities are using today will be specified as extensions to the Core API.

• Technologies that change more frequently are decoupled and specified in separate modules (“requirements classes” in OGC terminology). This enables, for example, the use/re-use of new encodings for spatial data or Web API definition (such as new version of the OpenAPI description document).

• Modularization is not just about a single “service”. OGC APIs will provide building blocks that can be reused in Web APIs in general. In other words, a server supporting the OGC API — Tiles should not be seen as a standalone service. Rather it should be viewed as a collection of Web API building blocks which together implement Tile capabilities. A corollary for this is that it should be possible to implement a Web API that simultaneously conforms to conformance classes from the Features, Coverages, Maps, Tiles, and other future OGC API standards.

This approach intends to support two types of client developers:

• Those that have never heard about the OGC. Developers should be able to create a client using the Web API definition without the need to adopt a specific OGC approach (they no longer need to read how to implement a GetCapabilities, allowing them to focus on the geospatial aspects).

• Those that want to write a “generic” client that can access OGC APIs. In other words, they are not specific for a particular Web API.

As a result of following a RESTful approach, OGC API implementations are not backwards compatible with OWS implementations per se. However, a design goal is to define OGC APIs in a way that an OGC API interface can be mapped to an OWS implementation (where appropriate). OGC APIs are intended to be simpler and more modern, but still an evolution from the previous versions and their implementations making the transition easy (e.g. by initially implementing facades in front of the current OWS services).

6.3.  Relationship to other OGC API standards

The OGC WMS and WMTS share the concept of a map and the capability to create and distribute maps at a limited resolution and size. In WMS, the number of rows and columns that a map should have can be selected by the user within limits, and in WMTS the number of rows and columns of the tile is predefined in the tile matrix.

With time, the concept of a tile, initially used for map tiles has been generalized to other data models such as feature data (some vendors use the expression vector tiles) and even to coverage data or processes that can be parallelized dividing the space in tiles. This standard presents an approach to tiles that can be applied to almost every resource type that returns geospatial data. If applied in conjunction with the OGC API — Features standard and on top of a feature collection, the expected result is tiled feature data. If applied in conjunction with the OGC API — Maps standard and on top of a collection that is transformed into a map by applying a style, the result should be map tiles (usually in PNG or JPEG format).

This standard can be referenced by other standards providing resources that that can be offered as tiles. For example:

• OGC API — Maps specifies the link relation types to access map tilesets from a dataset or collection.

• OGC API — Styles defines paths to list available styles from which tilesets can also be accessed.

• OGC API — Coverages specifies the link relation types and specifics of retrieving coverage tiles.

• OGC API — Processes — Part 3: Workflows and Chaining provides a mechanism to trigger localized processing workflows as a result of retrieving tiles (for a specific area and resolution of interest).

This document is the first part of a series of OGC API — Tiles “parts” that use the core and extensions model. It is foreseen that future parts will specify other extensions, such as how to get information of a point in a tile and how to retrieve multiple tiles in a single request. Other standards or extensions of standards may also provide mechanisms (e.g., additional query parameters) to deal with additional dimensions such as elevation, or more advanced temporal capabilities than what is defined in this standard’s datetime conformance class.

6.4.  Using this standard independently

Although this standard is designed as a building block that can be leveraged by other standards adding precisions about specific types of data available as tiles (e.g., OGC API — Maps and OGC API — Coverages), the conformance classes defined in this document are still concrete enough to make it possible to distribute and request various types of tiled data, including coverages, vector features and maps, by relying strictly on the content herein and in the 2D Tile Matrix Set and Tileset metadata 2.0 standard.

As informative guidance on how this can be achieved, implementations should consider the following aspects.

6.5.  How to approach an OGC API

There are at least two ways to approach an OGC API.

• Read the landing page, look for links, follow them and discover new links until the desired resource is found

• Read a Web API definition document that will specify a list of paths and path templates to resources.

For the first approach, many resources in the Web API include links with rel properties to know the reason and purpose for this relation. The following figure illustrates the resources as ellipses and the links as arrows with the link rel as a label.

Figure 2 — Resources and relations to them via links

For the second approach, implementations should consider the Clause 14 which specifies the use of operationID suffixes, providing a mechanism to associate API paths with the requirements class that they implement.

There is yet a third way to approach an OGC API that relies on assuming a set of predefined paths and path templates. These predefined paths are used in many examples in this document and are presented together in Table 8. It is expected that many implementations of this Standard will provide a Web API definition document (e.g. OpenAPI) using this set of predefined paths and path templates to get necessary resources directly. All this could mislead the reader into getting the false impression that the predefined paths are enforced. Therefore, building a client that is assuming a predefined set of paths is risky. However, it is expected that many API implementations will actually follow the predefined set of paths and the client using this approach could be successful in many occasions. Again, be aware that these paths are not required by this Standard.

Table 8 — Overview of resources and common direct links that can be used to define an OGC API — Tiles implementation

6.6.  Why we call them “tiles”

The word tile is traditionally used to refer to a thin, flat or convex slab of hard material such as baked clay or plastic, laid in rows to cover walls, floors, and roofs. In here, we are using the same approach to cover the viewport of a computer screen with tiles representing parts of the world (geospatial features). Actually, some examples of traditional tilesets representing geospatial features can also be found. They are tilesets with only one available tilematrix.

Figure 3 — Tiles in the floor of the monument of discovery in Lisbon, Portugal. (Lee Cannon April 2010, CC-BY-SA, https://www.flickr.com/photos/leecannon/5127274297)

Figure 4 — Tiles in the floor of the terminal 2 of the Prague Airport, Czech Republic. (Joan Masó, September 2022, CC0)

7.1.  A tile

A tile resource is a geospatial resource presenting a fragment of a more bigger geospatial data resource that is spatially constrained at the boundaries of the selected tile in a tile matrix set.

  name: tileMatrix
  in: path
  description: Identifier selecting one of the scales defined in the TileMatrixSet and representing the scaleDenominator the tile.
  required: true
  schema:
    type: string
  example: '11'

  name: tileRow
  in: path
  description: Row index of the tile on the selected TileMatrix. It cannot exceed the MatrixWidth-1 for the selected TileMatrix
  required: true
  schema:
    type: integer
    minimum: 0
  example: '827'

  name: tileCol
  in: path
  description: Column index of the tile on the selected TileMatrix. It cannot exceed the MatrixHeight-1 for the selected TileMatrix.
  required: true
  schema:
    type: integer
    minimum: 0
  example: 1231

  name: tileMatrixSetId
  in: path
  description: Identifier selecting one of the TileMatrixSetId supported by the resource.
  required: true
  schema:
    type: string
  example: 'WebMercatorQuad'

7.2.  Declaration of conformance classes

To support “generic” clients wishing to access multiple OGC API standards and extensions — and not “just” a specific Web API / server, the Web API has to declare the requirements classes it implements and conforms to.

{
  "conformsTo": [
    "http://www.opengis.net/spec/ogcapi-common-1/1.0/conf/core",
    "http://www.opengis.net/spec/ogcapi-tiles-1/1.0/conf/core"
  ]
}

8.1.  Overview

The tileset conformance class provides a mechanism to retrieve metadata for a set of tiles of geospatial data tiled according to one specific TileMatrixSet. It also provides a mechanism to obtain a templated link to retrieve individual tiles as defined in the core conformance class.

It describes the HTTP GET operation on a tileset resource and its response, but does not prescribe an specific path. The response provides metadata as per the 2D Tile Matrix Set and TileSet Metadata standard.

The essential elements of this metadata are:

• a link to the definition of the TileMatrixSet (either one registered in the OGC TileMatrixSet registry, or to a custom TileMatrixSet definition),

• a TileMatrixSet URI in the case of a TileMatrixSet registered with an authority (e.g. the OGC NA TileMatrixSet registry),

• a Coordinate Reference System (e.g. provided as a URI),

• a templated link (URI) to individual tiles,

• and a data type (indicating whether the tileset consists of vector, coverage or map tiles).

It may optionally also provide additional information, such as:

• a title,

• a description,

• the limits of the tileset if it does not span the full extent of the TileMatrixSet,

• the geospatial data resources involved in the creation of the tiles (potentially including links to OGC API collections),

• a schema of the available properties contained within the tiles,

• styles used to create the tiles,

• a central point on which a viewer may initially focus,

• attribution.

A link to a definition of a TileMatrixSet is always required whether a custom TileMatrixSet or a registered TileMatrixSet is used. It is recommended that the Web API hosts a local definition of each supported TileMatrixSet to ensure availability.

8.2.  Tileset resource

A tileset consists of a set of tiles obtained by partitioning geospatial data according to a particular TileMatrixSet. The tileset metadata contains all the information necessary for a client application to request tiles from the tileset.

{
  ...
  "tileMatrixSetURI": "http://www.opengis.net/def/tilematrixset/OGC/1.0/WorldMercatorWGS84Quad",
  "dataType": "map",
  "crs": "http://www.opengis.net/def/crs/EPSG/0/3395",
  "links": [
    ...
    {
     "href": "http://data.example.com/collections/buildings/tiles/WorldMercatorWGS84Quad",
     "rel": "self",
     "type": "application/json",
     "title": "Buildings tileset tiled using World Mercator TileMatrixSet"
    },
    {
     "href": "http://schemas.opengis.net/tms/2.0/json/examples/WorldMercatorWGS84Quad.json",
     "rel": "http://www.opengis.net/def/rel/ogc/1.0/tiling-scheme",
     "type": "application/json",
     "title": "Definition of WorldMercatorQuad TileMatrixSet"
    },
    {
     "href": "http://data.example.com/collections/buildings/tiles/WorldMercatorWGS84Quad/{tileMatrix}/{tileRow}/{tileCol}.png",
     "templated": true,
     "rel": "item",
     "type": "image/png",
     "title": "Templated link for retrieving PNG tiles"
    }
   ...
  ],
  "tileMatrixSetLimits":
  [
    { "tileMatrix" : "0", "minTileRow" : 0, "maxTileRow" : 0, "minTileCol" : 0, "maxTileCol" : 0 },
    { "tileMatrix" : "1", "minTileRow" : 0, "maxTileRow" : 0, "minTileCol" : 1, "maxTileCol" : 1 },
    { "tileMatrix" : "2", "minTileRow" : 1, "maxTileRow" : 1, "minTileCol" : 2, "maxTileCol" : 2 },
    { "tileMatrix" : "3", "minTileRow" : 3, "maxTileRow" : 3, "minTileCol" : 4, "maxTileCol" : 4 },
    ...
  ]
}

{
  ...
  "dataType": "map",
  "crs": "http://www.opengis.net/def/crs/EPSG/0/2001",
  "links": [
    ...
    {
     "href": "http://data.example.com/collections/buildings/tiles/CustomAntiguaTMS",
     "rel": "self",
     "type": "application/json",
     "title": "Buildings tileset tiled using custom Antigua TileMatrixSet"
    },
    {
     "href": "http://data.example.com/collections/buildings/tiles/CustomAntiguaTMS/{tileMatrix}/{tileRow}/{tileCol}.png",
     "templated": true,
     "rel": "item",
     "type": "image/png",
     "title": "Templated link for retrieving PNG tiles"
    },
    {
     "href": "http://data.example.com/tileMatrixSets/CustomAntiguaTMS",
     "rel": "http://www.opengis.net/def/rel/ogc/1.0/tiling-scheme",
     "type": "application/json",
     "title": "Definition of custom Antigua TileMatrixSet"
    }
   ...
  ],
  "tileMatrixSetLimits":
  [
    ...
  ]
}

8.3.  Web API-defined TileMatrixSets

This section provides more details on the recommendations for Web API-defined TileMatrixSets. In the future, an extension of this standard could describe a mechanism to manage (create, update…​) tiling schemes for a Web API and make some of the recommendations expressed here mandatory.

{
  "links": [
    ...
    {
      "href": "http://data.example.org/tileMatrixSets?f=json",
      "rel": "http://www.opengis.net/def/rel/ogc/1.0/tiling-schemes",
      "type": "application/json",
      "title": "List of tileMatrixSets implemented by this API in JSON"
    },
    {
      "href": "http://data.example.org/tileMatrixSets?f=html",
      "rel": "http://www.opengis.net/def/rel/ogc/1.0/tiling-schemes",
      "type": "text/html",
      "title": "List of tileMatrixSets implemented by this API in HTML"
    }
  ]
}

  type: object
  required:
    - tileMatrixSets
  properties:
    tileMatrixSets:
      type: array
      items:
        $ref: '#/components/schemas/id-link'

id-link:
  type: object
  description: |-
    Reusable object that contains an id to a resource and links where the object is described or a representation retrieved. Typically it is useful for paths like `/resources` and `/resources/{resourceId}`.   `/resources` will respond an array of id-link listing the `resourceId` and the links to get it. /collections and /collections/{collectionId} is an exception to this pattern.
    The fact that `links` is an array can be used to advertise the same object representation in different formats.
  required:
    - id
    - links
  properties:
    id:
      type: string
    tileMatrixSetURI:
      type: string
      format: uri
      description: If the Tile Matrix Set is registered in the Definitions Server, this property should the reference to this definition
    title:
      type: string
    links:
      type: array
      minItems: 1
      items:
        $ref: '#/components/schemas/link'

{
  "tileMatrixSets": [
    {
      "id": "MyWebMercatorQuad",
      "uri": "http://www.opengis.net/def/tilematrixset/OGC/1.0/WebMercatorQuad"
      "title": "My Google Maps Compatible for the World",
      "links": [
        {
          "rel": "self",
          "href": "https://data.example.org/tileMatrixSets/MyWebMercatorQuad",
          "type": "application/json",
          "title": "Local definition of WebMercatorQuad TileMatrixSet"
        }
      ]
    }
  ]
}

{
  "title": "My TileMatrixSet for the World",
  "id": "MyTMS",
  "uri": "http://www.opengis.net/def/tilematrixset/OGC/1.0/WebMercatorQuad",
  "crs": "http://www.opengis.net/def/crs/EPSG/0/3857",
  "wellKnownScaleSet": "http://www.opengis.net/def/wkss/OGC/1.0/GoogleMapsCompatible",
  "tileMatrices": [
    ...
    {
      "title": "My zoom level 3",
      "id": "3",
      "scaleDenominator": 69885283.0035897,
      "cellSize": 19567.8792410051,
      "pointOfOrigin": [-20037508.3427892,20037508.3427892],
      "tileWidth": 256,
      "tileHeight": 256,
      "matrixWidth": 8,
      "matrixHeight": 8
    }
    ...
  ]
}

9.1.  Overview

This class defines a resource called tilesets list that provides a list of available tilesets for a resource. It also defines a how to link to individual tileset resources, which are defined in the Clause 8. Refer to the Clause 10 and Clause 11 classes that describes two complementary mechanisms to associate tilesets to datasets and to geospatial data resources, respectively.

9.2.  Tilesets list

A tilesets list resource represents a list of sets of tiles, each one belonging to a particular TileMatrixSet. Each tileset resource returns the necessary metadata to enable a client application to formulate a tile request.

{
  "tilesets": [
    ...
    {
      "title" : "Buildings (WebMercatorQuad)",
      "tileMatrixSetURI" : "http://www.opengis.net/def/tilematrixset/OGC/1.0/WebMercatorQuad",
      "crs" : "http://www.opengis.net/def/crs/EPSG/0/3857",
      "dataType" : "vector",
      "links" : [
         {
           "rel": "self",
           "href": "http://data.example.com/collections/buildings/tiles/WebMercatorQuad",
           "type": "application/json"
         },
         {
           "rel": "http://www.opengis.net/def/rel/ogc/1.0/tiling-scheme",
           "href": "http://data.example.com/tileMatrixSets/WebMercatorQuad",
           "type": "application/json"
         }
      ]
   }
   ...
  ]
}

10.1.  Overview

This conformance class defines a mechanism to retrieve a list of tilesets for a dataset (a.k.a., a root resource) which may contain multiple geospatial data resources. It is used in conjunction with Clause 9 that specifies the response to this GET request.

Combined with the Clause 12 conformance class, it is also possible to select specific geospatial data resources (collections) to be combined and retrieved as tiles. For retrieving the list of tilesets for only one collection, the Clause 11 can also be used if it is implemented.

If a Web API offers several geospatial data resources for a dataset, it may limit the number of collections that can be retrieved together, and/or provide a limited subset of the collections by default.

10.2.  General

This building block stays flexible and does not require implementation of OGC API — Common — Part 1, allowing for other Web API architectures outside the OGC API framework to adopt it. However, a server implementing other OGC APIs is expected to implement OGC API — Common — Part 1. In practice, this means that the landing page and the conformance page follow OGC API — Common — Part 1 requirement classes when used. It is also possible to combine this building block with OGC API — Features — Part 1: Core, version 1.0.

10.3.  Web API landing page

The landing page provides links to start exploring the resources offered by the Web API. It mainly consists of a list of links to root resources. This conformance class requires including in the landing page one or more link(s) to list(s) of tilesets available for the dataset.

{
  "links": [
    ...
    {
       "href": "http://data.example.org/tiles",
       "rel": "http://www.opengis.net/def/rel/ogc/1.0/tilesets-vector",
       "type": "application/json",
       "title": "List of available vector features tilesets for the dataset"
    },
    {
       "href": "http://data.example.org/tiles",
       "rel": "http://www.opengis.net/def/rel/ogc/1.0/tilesets-map",
       "type": "application/json",
       "title": "List of available map tilesets for the dataset"
    }
  ]
}

10.4.  Dataset tilesets

The dataset tilesets operation provides essential tileset metadata and links to tilesets resources allowing to request tiles from the dataset.

10.5.  Tiles

The Clause 7 defines how to retrieve a single tile from a tileset available for the dataset.

11.1.  Overview

This conformance class assumes that data is organized into one or more geospatial data resources (e.g., the “collections” OGC API — Common — Part 2: Geospatial data). Geospatial data resources are referenced using URIs.

It defines how to specify link(s) to one or more list(s) of tilesets containing a representation of this geospatial data resource (path). It is used in conjunction with Clause 9 that specifies the response to this GET request.

11.2.  General

This building block depends on OGC API — Part 2: Geospatial data, but stays flexible and does not require implementation of OGC API — Common — Part 1, allowing for other Web API architectures outside the OGC API framework to adopt it. However, a server implementing other OGC APIs is expected to implement OGC API — Common — Part 1. In practice, this means that the landing page and the conformance page follow OGC API — Common core requirement classes when used. It is also possible to combine this building block with OGC API — Features — Part 1: Core, version 1.0 instead of _OGC API — Common — Part 2.

11.3.  Geospatial data resources

This standard does not specify how geospatial data resources are exposed in the Web API and if they can be retrieved as geospatial data (e.g., feature items). For example, OGC API — Features — Part 1: Core, version 1.0 includes the definition of collections and each collection is available in the /collections/{collectionId} path. OGC API — Common will provide a similar mechanism. Other paths in the Web API could also give access to geospatial data resources.

For example, an implementation of the OGC API — Features — Part 1: Core returns a list of links that include geospatial aspects for each geospatial data resource in the /collections/{collectionId} path. OGC API — Common — Part 2: Geospatial data provides a similar mechanism. In the JSON response, the links array is where links to lists of tilesets must be added.

Example — Fragment of a collection with a links array including two items pointing to lists of tilesets (one for vector tiles and one for map tiles)

[
  ...
  {
    "id": "buildings",
    "title": "Buildings in the city of Bonn",
    "description": "This collection contains buildings",
    "attribution": "OpenStreetMap",
    "extent": {
      ...
    }
    "links": [
      ...
      {
        "href": "http://data.example.com/collections/buildings/tiles",
        "rel": "http://www.opengis.net/def/rel/ogc/1.0/tilesets-vector",
        "type": "application/json",
        "title": "List of available vector tilesets for the collection of Bonn buildings"
      },
      {
        "href": "http://data.example.com/collections/buildings/tiles",
        "rel": "http://www.opengis.net/def/rel/ogc/1.0/tilesets-map",
        "type": "application/json",
        "title": "List of available map tilesets for the collection of Bonn buildings"
      }
    ]
  }
  ...
]

11.4.  Geospatial data resources tilesets list

The geospatial data resource tilesets operation provides essential tileset metadata and links to tilesets resources allowing to request tiles from the resource.

11.5.  Tiles

A tile resource is a fragment of a larger single geospatial data resource that is spatially constrained at the boundaries of the selected tile in a tile matrix set. Details of the operation are described in the Clause 7.

12.1.  Overview

In a Web API providing access to a complex dataset formed by several geospatial data resources, it can be useful to select specific sub-resources of interest when requesting data from this dataset. This requirements class defines how to include a query parameter when requesting a resource (e.g., dataset tiles) to specify which geospatial data resources (a.k.a. collections) should be used to generate the response.

This conformance class can be used e.g. in conjunction with the Clause 10 conformance class or in conjunction with an equivalent conformance class in OGC API — Maps.

12.2.  Operation

By default, the geospatial data resources to be included in the dataset tiles responses are unspecified but should represent the dataset as a whole. This class adds a mechanism to select the geospatial data resources to be used to generate the derived resources (e.g., maps or tiles). In practice this enables the capability to generate resources involving more than one geospatial data sub-resource.

  name: collections
  in: query
  required: false
  style: form
  explode: false
  schema:
    type: array
    items:
      type: string

13.1.  Overview

This conformance class defines the way date and time can be used as a parameter to filter the content in the tile resource. This conformance class is importing most of the functionality from OGC API — Commons.

13.2.  Describing the temporal extent

Depending on the type of resource, the way the temporal extent and the resolution of the datetime values available for the client to request are described may be different:

• For Geodata Tilesets, the collection description should specify the temporal extent of the resources. Tiles can be requested inside this extent. If the extent is specified in a way that instant values are provided (e.g. by listing them or by including a resolution) then it be possible to request tiles for these instants.

• If a tileset metadata is available, a future revision of 2D tile matrix set standard could take precedence providing more details on the available values for datetime.

13.3.  datetime query parameter request and response

This section is based on the OGC API common datetime module that is entirely reproduced here.

The datetime parameter selects resources based on their temporal extent. The definition of temporal extent is specific to the resource type being filtered.

The datetime parameter is defined as follows:

name: datetime
in: query
required: false
schema:
  type: string
style: form
explode: false

interval-closed     = date-time "/" date-time
interval-open-start = [".."] "/" date-time
interval-open-end   = date-time "/" [".."]
interval            = interval-closed / interval-open-start / interval-open-end
datetime            = date-time / interval

While the processing of the datetime parameter is specific to the resource and operation for which it is applied, there is a general set of requirements which all implementations must address.

“Intersects” means that the time (instant or period) specified in the parameter datetime includes a timestamp that is part of the temporal geometry of the resource (again, a time instant or period). For time periods this includes the start and end time.

Table 10

Example 1 — A date-time

For resources with a temporal property that is a timestamp (like lastUpdate), a date-time value would match all resources where the temporal property is identical.

For resources with a temporal property that is a date or a time interval, a date-time value would match all resources where the timestamp is on that day or within the time interval.

Example 2 — Intervals

A template for the definition of the parameter in YAML according to OpenAPI 3.0 is available at datetime.yaml.

13.4.  subset=datetime query parameter request and response

The behavior of the subset parameter is imported from the OGC API — Common subset module. The entire module is reproduced here. However, some considerations may not apply for datetime and the generic behavior is limited by predetermining the axis name of the generic datetime in an additional requirement, a permission and a recommendation at the end of this subsection.

The subset parameter is used to select a subset of a geospatial resource.

The subset parameter is defined as follows:

  SubsetSpec:       "subset"=axisName(intervalOrPoint)
  axisName:         {text}
  intervalOrPoint:  interval \| point
  interval:         low : high
  low:              point \| *
  high:             point \| *
  point:            {number} \| "{text}"

  Where:
     \" = double quote = ASCII code 0x42,
     {number} is an integer or floating-point number, and
     {text} is some general ASCII text (such as a time and date notation in ISO 8601).

While the processing of the subset parameter is specific to the resource and operation for which it is applied, there is a general set of requirements which all implementations must address.

Example 1 — A date-time (subset)

For resources with a temporal property that is a timestamp (like lastUpdate), a date-time value would match all resources where the temporal property is identical.

For resources with a temporal property that is a date or a time interval, a date-time value would match all resources where the timestamp is on that day or within the time interval.

Example 2 — Intervals (subset)

13.5.  Actual date & time response header

interval     = instant "/" instant
datetime     = instant / interval

13.6.  Closest date & time permission

14.1.  Overview

This conformance class defines particularities of providing a definition of a Web API implementing this standard using OpenAPI Specification version 3.0.

14.2.  Web API OpenAPI description

The OpenAPI definition provides a description of the complete list of API resources. Reading this description, an application will have the full picture of the resources that the API provides, how to retrieve them, and what responses are expected for successful and unsuccessful requests. Without this API description an application will be forced to traverse all links starting by the landing page to get an equivalent full list of resources.

The OGC API — Common — Part 1: Core (oas30) requirement class provides many details on general requirements that this requirements class adopts by dependency. In addition extra requirements are provided. Also, the OGC API — Common requirement class provides details on how to request an API definition.

15.1.  Overview

This standard provides several resources describing the service (landing page), the geospatial data resources, the tileset lists and the tilesets informing the client on how to retrieve tiled data. XML is a data-interchange format designed to facilitate structured data interchange between applications. The intention of this section is to define an XML encoding that could be implemented by Tiles Web APIs, but not to exclude the possibility of defining additional metadata encodings that may be offered by a Tiles Web API. Web APIs may adopt this XML conformance class and declare conformance to it in the list of conformance classes supported by the Web API. The declaration of XML in the conformance classes supported does not mean that all the resources provided by the Web API support an XML representation, but a general support of XML is expected.

This clause specifies a requirements class for an XML representation that may be implemented by an OGC Web API for the tilesets list and a tileset resources in addition to the JSON representation required by Clause 8 and Clause 9.

If the service provides local TileMatrixSet definitions, it is recommended that those resources also support an XML representation conforming to the XML schema specified in the Two Dimensional Tile Matrix Set and Tileset Metadata standard.

Please refer to OGC API — Common conformance classes defining the XML representation of common resources such as the landing page, conformance and collections.

15.2.  TileSet and TileSets List XML representation

16.1.  Overview

This clause specifies six pre-defined requirements classes for encodings to be used by the tiles of the OGC API implementation:

• PNG

• JPEG

• TIFF

• NetCDF

• GeoJSON

• Mapbox Vector Tiles

16.2.  Requirement Class “PNG”

One fundamental use case for tiles is immediate visualization in a web browser. In these circumstances, selecting an encoding that can be natively interpreted by the web browser is fundamental. The PNG is one of the most popular formats in de web defined by the ISO Information technology — Computer graphics and image processing — Portable Network Graphics (PNG): Functional specification. ISO/IEC 15948:2003 (E), also available by the W3C in https://www.w3.org/TR/PNG.

PNG supports lossless data compression. PNG supports palette-based images (with palettes of 24-bit RGB or 32-bit RGBA colors), grayscale images (with or without an alpha channel for transparency), and full-color non-palette-based RGB or RGBA images. The PNG working group designed the format for transferring images on the Internet, not for professional-quality print graphics; therefore non-RGB color spaces such as CMYK are not supported.

16.3.  Requirement Class “JPEG”

One fundamental use case for tiles is immediate visualization in a web browser. In these circumstances, selecting an encoding that can be natively interpreted by the web browser is fundamental. The JPEG is one of the most popular formats in de web defined by the ITU-T Recommendation T.81 and the ISO/IEC 10918-1.

The JPEG compression algorithm operates at its best on photographs and paintings with smooth variations of tone and color. It is best used for color and grayscale still images, but not for binary images. JPEG is also the most common format saved by digital cameras. However, JPEG is not well suited for line drawings and other textual or iconic graphics, where the sharp contrasts between adjacent pixels can cause noticeable artifacts. Such images are better saved in a lossless graphics format such as PNG. Because JPEG is a lossy compression method, which reduces the image fidelity, it is inappropriate for exact reproduction of imaging data.

16.4.  Requirement Class “TIFF”

One use case for tiles is to distribute fragmented coverage values as regular grids. In these circumstances, selecting an encoding that is able to story grid values in their original format and eventually compress them using lossless compression is the right solution. The TIF is one of the older formats but still one of the most popular formats to preserve arrays of data values and defined by the TIFF v6 specification owned by Adobe Systems.

TIFF is a flexible, adaptable file format for handling images and data. The ability to store data in a lossless format makes a TIFF file a useful image archive, because, unlike standard JPEG files, a TIFF file using lossless compression such as PackBits or LZW compression.

16.5.  Requirement Class “NetCDF”

For a case of multidimensional regular grid tiles, as defined in Annex J of the 2D-TMS Standards [OGC 17-083r4], there is a need for a format able to store multidimensional data in a natural way. The NetCDF is one of the most popular formats for scientific data that is able store multi-dimensional arrays of data values. It is defined by the UCAR-Unidata.

16.6.  Requirement Class “GeoJSON”

GeoJSON is a commonly used format for representing features with geometries and other properties. It is simple to understand and well supported by tools and software libraries. Since most Web developers are comfortable with using a JSON-based formats supporting GeoJSON is recommended for vector tiles, if the feature data can be represented in GeoJSON for the intended use.

16.7.  Requirement Class “Mapbox Vector Tiles”

Mapbox Vector Tiles is a well known format for representing features with geometries in tile [15]. The Mapbox Vector Tile format uses Google Protocol Buffers as a encoding format. Protocol Buffers are a language-neutral, platform-neutral extensible mechanism for serializing structured binary data. A Mapbox Vector Tile represents data based on a square extent within a tile matrix set. However, a Mapbox Vector Tile does not contain information about its bounds and TileMatrixSet. The file format assumes that the client knows the bounds and TileMatrixSet of the file before decoding it.